The term “battery” originally means a plurality of electrochemical cells connected in series. However, nowadays individual electrochemical cells (individual cells) are very frequently also understood to be batteries.
Batteries with the design mentioned above are frequently cells in which an alkali metal, in particular lithium, is used as the active material in the negative electrode. Examples of batteries with a negative lithium electrode are a lithium thionylchloride battery, lithium sulphur dioxide battery, lithium carbon monofluoride battery, lithium iron sulphide battery and lithium manganese dioxide battery. In the last-mentioned lithium manganese dioxide battery, manganese dioxide electrodes are used as the positive electrode, in a lithium iron sulphide battery, iron disulphide electrodes are used as the positive electrode, and in a lithium sulphur dioxide battery, sulphur dioxide dissolved in acetonitrile (absorbed in an inert electrode) is used as the positive electrode. In that context, the positive electrodes are often designed as hollow cylinders. The negative lithium electrode is arranged in the interior of the positive electrode, surrounded by a separator that separates the positive electrode from the negative electrode, but at the same time permits the transfer of ions between the two electrodes. The transfer of ions is generally ensured by the use of a suitable electrolyte. For batteries with lithium electrodes, in particular electrolytes in which a salt such as, for example, lithium hexafluorophosphate is dissolved in an organic solvent, for example, in a carbonate, are particularly suitable.
The electrical contact with the positive electrode generally doesn't constitute a problem. Its outside is usually in direct contact with the inner wall of an electrically conductive battery housing part. The electrical contact can be made correspondingly via this housing part. In contrast, formation of contact with the negative electrode is more complex. A pin which is tapered to a point in a conical fashion at one end and has at the other end a flange which plays a role in the sealing of the housing is conventionally used for this. A typical example of such a current collector can be found in DE 32 40 806 A1.
A problem that occurs repeatedly with the described batteries is the occurrence of internal short-circuits. Lithium ions dissolved in the electrolyte can become deposited to form dendrites on the negative current collector. Such formation of dendrites is a problem, in particular, when temperature differences occur inside a battery, for example, as a result of local heating by an external heat source or as result of local cooling if part of the battery is in direct contact with a good conductor of heat. The dendrites grow over time and starting from a certain size they can enter into direct contact with the positive electrode, which causes the abovementioned short-circuits.
A known solution to that problem is to install the negative electrode in the form of a hollow cylinder. Deposition of lithium then occurs in particular in the interior of the hollow cylinder. As a result, short-circuit problems are effectively counteracted, but the basic problem of the deposition of lithium from the electrolyte on negative current collectors is not solved. In addition, the described measure has a negative effect on the energy density of batteries in question.